Wireless communications occur in an environment with unpredictable interference and channel variations. HARQ (Hybrid Automatic Repeat Request) is a common technique used to address the unpredictable interference and channel variations. HARQ involves a wireless device receiving an uplink or downlink transmission to attempt to decode a data message in the transmission.
FIG. 1 is a signaling diagram of a conventional HARQ technique employed between transmitting node 105 and receiving node 110 in an LTE system. Initially, the transmitter 105 transmits up to two transport blocks in a TTI (Transmission Time Interval) to receiving node 110 (step 115). An example of this transmission is illustrated in FIG. 2 in which TTI1 includes two transport blocks and TTI2 includes two transport blocks. Receiving node 110 then determines whether each of the two transport blocks was successfully received (step 120). Because LTE (Long Term Evolution) provides for up to two transport blocks per TTI, the receiving node 110 transmits a HARQ-ACK (ACKnowledgement) consisting of 2 bits, each bit indicating success or failure of a respective transport block, to the transmitting node 105 (step 125).
The transmitter then determines, based on the value of the bits in the HARQ-ACK, whether one or more transport blocks were not successfully decoded (step 130). If so, the transmitting node 105 transmits the unsuccessfully decoded transport block(s) to the receiving node 110 (step 135). The receiving node 110 then attempts to decode the unsuccessfully decoded transport block by soft combining it with the retransmitted transport block (step 140). The type of soft combining can vary, and can involve the well-known Chase or Incremental Redundancy soft combining techniques. Soft combining greatly increases the probability of successful decoding.
LTE, which is a standard in 3GPP family of wireless systems, is highly optimized for MBB (Mobile BroadBand) traffic. The TTI (subframe) has duration of 1 ms and, for FDD (Frequency Division Duplex) the HARQ-ACK is transmitted in subframe n+4 for a data transmission in subframe n.
URLLC (Ultra-Reliable Low Latency Communication) is data service with extremely strict error and latency requirements, including error probabilities as low as 10−5 or lower and end-to-end latency or lower 1 ms. Other services have similar error and latency requirements, such as the so-called short TTI in LTE.
Although the fifth generation of mobile telecommunications and wireless technology is not yet fully defined, it is in an advanced draft stage within 3GPP and includes work on 5G New Radio (NR) Access Technology. Accordingly, it will be appreciated that although LTE terminology is used in some portions of the disclosure, the disclosure equally applies to equivalent 5G entities or functionalities despite the use of terminology differing from what is specified in 5G. 3GPP TR 38.802 V1.0.0 (2016 November) provides a general description of the current agreements on 5G New Radio (NR) Access Technology and final specifications may be published inter alia in the future 3GPP TS 38.2** series.
MBB or eMBB (enhanced MBB) and URLLC are both among a wide range of data services being targeted for 5G. To enable services with an optimized performance, the TTI lengths are expected to be different for different services, wherein a TTI may correspond to a subframe, a slot, or a mini-slot. Specifically, URLLC may have a shorter TTI length compared to MBB.
Accommodating both MBB and URLLC in the same network introduces conflicts due to the strict latency requirements of URLLC. These conflicts can result in problems decoding either or both of the MBB and URLLC data when the data needs to be transmitted at the same time. Although HARQ is a common way of addressing decoding problems, implementing HARQ in a network accommodating both MBB and URLLC can be difficult due to the strict latency requirements of URLLC. Specifically, although conventional HARQ procedures can be implemented for the MBB data, conventional HARQ procedures likely cannot meet the strict latency requirements of URLLC data.